Background: rebuilding a motor for the REPU. New 84-85 GSL-SE rotor housings, new S5 rotors, new 3 piece apex seals. 4 port Streetport, 3b end plates, 12a intermediate plate, weekend driver + some autocrosses.

I measured two new 3-piece apex seals and they were 80.10mm long. My rotor housings narrowest points are 80.0020mm and 80.0049mm. The How to Modify your RX7 book says to sand the apex seals down to 79.90mm length for street use. Some people don't clearance the length of new Mazda seals and say they're fine as new. Other people say to clearance it 0.0015" narrower than rotor housing width. And others still say clearance it 0.004" to 0.0045" narrower than rotor housing width. Who is right?

The triangle piece is super glued to the upper piece. Should I super glue the lower piece to the rest of the apex seal, to make it all into a one piece? So I can sand it all as one piece and get a uniform cut on the apex seal? How thick is the super glue between the top piece and the triangle piece, should I subtract that out when computing the length?

Also, I assume I don't sand the triangle piece. Just sand the other end(s).

 

No, don't sand the triangle piece, but DO clearance your seals. There's no ONE way to clearance them, but you do NOT want them as wide or wider than your housings, that's asking for trouble. The seals NEED to be allowed to expand, if not you could lock your new motor and then guess what you have to do all over again... not to mention buy new major motor parts. How MUCH clearance you give them will depend on your application mostly. Generally you'll want closer/tighter tolerance for non-turbo (NA) applications, and greater/looser tolerance for forced induction.

But... I am a little confused. 13B rotors with 12A irons? And new 3 piece apex seals? WTH?

 

Makes sense but why do I hear so many people say not to clearance the length?

13b rotors, 13b rotor housings, 3b 13b end plates, 12a intermediate plate. Like a pack of lifesavers.

I ordered new apex seals from Mazda in January and they sent the 3 piece ones. Others have had this happen too recently. No option to buy 2 or 3 piece from Mazda, apparently they're switching back to that design.

 

Clearancing the length IS critical for one piece or long-corner two piece seals.

For Mazda OEM seals where the corner piece is just a triangle, it is not as critical, since the gap opened up when the triangle piece slides up is minimal. I have a feeling Mazda made the seals deliberately over-long so that the seals would go a long time before the corner piece even made contact with the rotor housing.

For a standard rebuild, I'd just follow the service manual's recommendations.

 

just drop them ***** in. worry more about your side seal clearance.

 

Advice to live by arghx
"Just drop them ***** in"

 

Well that's the thing, the service manual doesn't go over clearancing apex seal length. Just checking height. I'm hesitant to install it without sanding it shorter. Having the seal 0.1mm wider than what it slides around, with a spring under it to push it outward and up, at 8500rpm just doesn't sound right.

 

http://foxed.ca/rx7manual/manuals/ho...7RotorMods.pdf

Your welcome

 

Thanks but I have that book and referenced it in post 1. I think that section is referencing one piece carbon seals, especially with that wide a gap and saying that's what Downing used in Camel Lights.

It sounds like very few people measure let alone clearance apex seal length. I called Mazda Comp and they didn't know. The are exchangine my 3 piece seals with 2 piece FOR FREE. But of course I need to know what length to sand those to now..........

 

The rotor housing thickness might not be the 'exact' width of the combustion chamber.
You might want to consider the thickness of the compressed and countersunk o-rings and the dimension from side housing to side housing, not rotor housing width... maybe??

 

No.

 

just drop them ***** in

 

agree. iirc they don't do this in the DIY.RE13B video. If you were building a 1000hp 4 rotor or something I could understand maybe messing with it but if this is a street car just drop them in and roll.